| The basicranial circulation of Ptomacanthus resembles that in arthrodire placoderms. |
| The basicranial axis is straight, and the fontanelle in the lachrymal region is very large. |
| In front of the presphenoid the basicranial axis is continued by the mesethmoid. |
| The posterior part of the craniofacial axis, which has relations only with the cranium, is called the basicranial axis. |
| Of these, one of the largest is the parasphenoid which, in Ichthyopsids, is found underlying the basicranial axis. |
| Some of the most important structural features that mark it as such are in the basicranial region. |
